Dynamic axial preloading with flexure plate

ABSTRACT

A system for an unmanned aerial vehicle can include an altitude control system, which further includes a compressor assembly, a valve assembly, and an electronics assembly. The compressor assembly may include a driveshaft and a bearing assembly configured to rotate the driveshaft. The driveshaft may be formed from a first material and a compressor housing may be formed from a second material. The first and second materials may have different rates of thermal expansion. A dynamic preloading mechanism, such as a flexible plate, may be provided within the compressor assembly to exert a preloading force on the bearing assembly. Throughout the duration of the flight of the unmanned aerial vehicle, the preloading mechanism can continually compensate for differences in rates of thermal expansion between the first and second materials throughout.

CROSS-REFERENCES TO RELATED APPLICATIONS

The present application claims the benefit of the filing date of U.S.Provisional Application No. 62/782,129 filed on Dec. 19, 2018 and U.S.Non-Provisional patent application Ser. No. 16/442,733 filed Jun. 17,2019, the disclosures of which are incorporated by reference.

BACKGROUND

Unmanned aerial vehicles, such as balloons, may operate at substantialaltitudes. Such vehicles may operate within the Earth's stratosphere,having favorably low wind speeds at an altitude between 18 and 25 km(11-15 mi). Wind speed and wind direction vary at certain altitudes,allowing unmanned vehicles to rely on the wind speed and wind directionalone for navigation, without the need for additional propulsion means.Unmanned vehicles must therefore increase or decrease their altitude tochange course or to increase speed.

BRIEF SUMMARY

Aspects of the present disclosure are advantageous for high altitudeballoon systems, For instance, one aspect of the disclosure provides fora system that includes an altitude control system for an aerial vehicle.The altitude control system further includes a compressor assembly thatincludes a compressor housing, a motor housing, a drive shaft, a motor,a bearing assembly, and a flexible plate. The compressor housing caninclude a cavity that extends therethrough. The compressor housing canbe comprised of a first material. The motor housing may be disposedwithin the compressor housing. The driveshaft may extend through themotor housing and the driveshaft may be comprised of a second material.The motor may be coupled to a driveshaft and disposed within the motorhousing. The bearing assembly can be configured to provide axialrotation of the driveshaft. The flexible plate may be coupled to themotor housing and the bearing assembly. A coefficient of thermalexpansion of the first material can differ from a coefficient of thermalexpansion of the second material. The flexible plate may be configuredto compensate for differences in rates of thermal expansion between thefirst and second materials by applying a preloading force to the bearingassembly that changes in response to changes in temperature.

In one example, the bearing assembly can be a ball bearing assembly thatincludes a first inner race directly adjacent the driveshaft and asecond outer race spaced away from the first inner race. The flexibleplate may be directly adjacent to the second outer race. The flexibleplate may apply the preloading force to the second outer race when theflexible plate compensates for differences in thermal expansion. In someexamples, the flexible plate can further include a bearing seat. Thebearing assembly can be positioned within the bearing seat and thebearing seat of the flexible plate can apply the preloading force to thesecond outer race. The bearing seat can further include acircumferential wall that extends upwardly from a surface of theflexible plate and forms a circumferential perimeter around a portion ofthe surface of the flexible plate. The bearing seat can be sized tosecure the bearing assembly within the circumferential wall.

In another example, the bearing seat can transition from a firstdiameter adjacent a surface of the flexible plate to a second diameterthat is greater than the first diameter. An interior ridge can be formedat the transition between the first and second diameters. The bearingassembly can contact the interior ridge. The flexible plate can beattached to the motor housing. In some examples, the flexible plate isattached to the motor housing along a perimeter of the flexible plate.

In another example, the system further includes an impeller coupled toan end of the driveshaft. The impeller can be configured to draw airinto the compressor housing. The compressor housing can further includean inlet and an outlet. The impeller may be positioned at the outlet andthe motor housing may overlie the impeller.

In yet another example, the system further includes an outer envelopeconfigured to retain lift gas therein and an inner envelope disposedwithin the outer envelope. The inner envelope can be configured toretain a ballast gas therein, wherein the compressor assembly regulatesan amount of air within the inner envelope.

In still another example of this aspect, the system further includes anouter envelope and an inner envelope disposed within the outer envelope.The outer envelope may be configured to retain a ballast gas therein.The compressor assembly can regulate an amount of air within the outerenvelope.

In another example, the motor housing is open at one end and includes anopening. The flexible plate can extend across the opening, so as toenclose an interior space of the motor housing.

Other aspects of the disclosure include a system. The system includes analtitude control system for an aerial vehicle. The altitude controlsystem further includes a compressor assembly and a flexible plate. Thecompressor assembly includes a compressor housing having a cavityextending therethrough; a motor housing disposed within the compressorhousing; a driveshaft extending through the motor housing; a motorcoupled to a driveshaft and disposed within the motor housing; a bearingassembly configured to provide axial rotation of the driveshaft; and aflexible plate. The flexible plate may be attached to an end of themotor housing and coupled to the bearing assembly. When the flexibleplate is in a first position, the flexible plate may be spaced a firstfixed distance from the motor housing and the flexible plate applies afirst preloading force to the bearing assembly. In response to a changein temperature, the flexible plate may be configured to move into asecond position where the flexible plate is a second fixed distance awayfrom the motor housing that is less than the first fixed distance, theflexible plate applying a second preloading force to the bearingassembly in the second position that is different than the firstpreloading force.

In one example, the bearing assembly is a ball bearing assembly thatincludes a first inner race directly adjacent the driveshaft and asecond outer race spaced away from the inner race. The flexible platemay be directly adjacent the second race and apply the preloading forceto the second outer race when the flexible plate compensates fordifferences in thermal expansion.

In one example, the flexible plate can further include a bearing seat.The bearing assembly may be positioned within the bearing seat. Thebearing seat of the flexible plate can apply the preloading force to thesecond outer race. The bearing seat can include a circumferential wallextending upwardly from a surface of the flexible plate and form acircumferential perimeter around a portion of the surface of theflexible plate. The bearing seat can be sized to secure the bearingassembly within the circumferential wall.

In another example, the bearing seat can transition from a firstdiameter closer to the surface of the flexible plate to a seconddiameter that is greater than the first diameter, An interior ridge canbe formed at the transition between the first and second diameters. Thebearing assembly can contact the interior ridge.

In yet another example of this aspect, the system further includes anouter envelope and an inner envelope disposed within the outer envelope.The outer envelope may be configured to retain a ballast gas therein,wherein the compressor assembly regulates an amount of air within theouter envelope.

In an alternative example, the system further includes an outer envelopeconfigured to retain a lift gas therein and an inner envelope disposedwithin the outer envelope. The inner envelope may be configured toretain a ballast gas therein. The compressor assembly can regulate anamount of air within the inner envelope.

In another example, the compressor assembly can further comprise animpeller coupled to the driveshaft, and the motor housing overlies theimpeller.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a functional diagram of a system in accordance with aspects ofthe present disclosure.

FIG. 2 is an example of a balloon in accordance with aspects of thepresent disclosure.

FIG. 3 is an example of a balloon in flight in accordance with aspectsof the disclosure.

FIG. 4 is an example altitude control system in accordance with aspectsof the disclosure.

FIG. 5 is an air compressor in accordance with aspects of thedisclosure.

FIG. 6 is cross-sectional view taken along line A-A of FIG. 5 .

FIG. 7 is an enlarged view of a portion of FIG. 6 ;

FIG. 8 is an enlarged view of a portion of FIG. 7 ;

FIG. 9 is an enlarged view of apportion of FIG. 6 .

FIG. 10 is an enlarged view of a portion of FIG. 6 .

DETAILED DESCRIPTION Overview

Altitude control systems may be implemented within unmanned vehicles toincrease or decrease the altitude of the unmanned vehicle. Such altitudecontrol systems can include several assemblies, including: (1) an aircompressor assembly; (2) a valve assembly, and (3) a control electronicassembly. Each of these components can cooperate to regulate the amountof air and/or gases into and out of the unmanned vehicle, so as toincrease or decrease the altitude of the unmanned vehicle, such as astratospheric balloon.

When implementing an altitude control system in a balloon, weight isparamount. The altitude control system must be made from durablematerials capable of withstanding extreme temperature change and harshenvironmental conditions. However, to ensure that the weight of thealtitude control system does not adversely affect balloon flight andlift, the selected materials cannot be too heavy. The housings and themajority of the components of the altitude control system are thereforetypically comprised of a light weight material, such as aluminum.Aluminum has the added advantages of being naturally corrosionresistant, ductile, and capable of maintaining the structure of thehousings. Moreover, aluminum is approximately one-third the density ofsteel, such that aluminum parts can be made thicker to increase theirstrength, while still allowing for an overall reduction in weight of thevehicle.

To enable manufacture of an altitude control system small enough to beused with an envelope of an unmanned aerial vehicle, a driveshaft madeof steel can be implemented within the compressor assembly of thealtitude control system. A driveshaft made from a lighter materialhaving a coefficient of thermal expansion that can match the remainderof the altitude control system, such as aluminum, would have anexcessive diameter necessary to provide the strength and stiffness ofsteel and would not be practical to employ. The result is an altitudecontrol system with a shaft that expands and contracts at a differentrate than the majority of the altitude control system.

The mismatched coefficients of thermal expansion of steel and aluminumcoupled with backpressure from within the balloon envelope, and theextreme temperature changes caused by the surrounding environment athigh altitudes, may lead to failure of the altitude control system. Inmany instances, the bearings of the bearing assemblies become unloaded,which may lead to catastrophic failure. Similarly, because the altitudecontrol system must operate at very high rotational velocities, criticalshaft rotor dynamic mode may occur inside the operating range of thedevice and may also lead to catastrophic failure.

The uncontrollable temperature changes that cause expansion andcontraction of these components at different rates throughout theduration of the balloon flight, make it difficult to predict and providefor a preloading force that can be dynamically applied to the bearingassembly. The solution to address these issues has been to carefullymachining the compressor and shaft assembly components to specifictolerances to accommodate expansion and contraction of these materials.This procedure is time consuming, costly, and complex, both in terms ofdetermining the appropriate tolerances, as well as machining componentswithin the predefined tolerances. In addition, such procedure providesmany possibilities for failure since the tolerances must be accuratelydetermined for each individual component, and the failure at any one ofthese components will result in overall failure of the altitude controlsystem. Moreover, tolerancing components of the altitude control systemis limited to the exact ranges of tolerances provided; any conditionwhich puts the system outside of this predetermined tolerance may verylikely result in failure of the altitude control system.

To address such failures, a dynamic axial preloading mechanism can beintegrated inside the motor housing of a device, such as an aircompressor, and that can maintain bearing preload of a rotating shaftassembly in order to achieve a long-lasting device when ongoingmaintenance cannot be performed. Bearing preload can be critical toextend the life of the rotating shaft assembly of a motor within theunmanned aerial vehicle, which must fly for the duration of its lifewithout returning to the ground. In accordance with aspects of thedisclosure, axial support, in combination with dynamic preload canaddress shortcomings related to backpressure from within an envelope,mismatched coefficient of thermal expansion, and extreme temperaturechanges caused by the environment surrounding the aerial device. Suchaspects help to eliminate the manufacture of individual components thatseparately address these shortcomings.

An example altitude control system may include a dynamic axialpreloading mechanism for the rotating shaft assembly of a compressor ofan unmanned aerial vehicle. A rotating driveshaft may be coupled at oneend to an impeller and a second end to a distal bearing assembly. Thepreloading mechanism can include a backplate which supports and seatsthe distal bearing assembly. The backplate may be flexible and movableto exert a continuous force on the distal bearing assembly. For example,the backplate may flex in response to changes in temperature. Further,the motor housing can be integrated with the overall structure of thealtitude control system so as to allow for the motor to berigidly/stiffly held in place, This can help to improve stiffness whichis critical to keeping the critical shaft modes outside/above theoperating range of the device.

When in use, as the environment changes, the backplate may flex andpress on the bearing assembly to keep the bearing assembly preloaded andengaged. This can help to prevent the catastrophic failure that wouldresult from unloading the bearing at high speed. The backplate thereforecompensates for changes in atmosphere, backpressure, temperature, etc.that would otherwise affect the bearing assembly.

Thus, the features disclosed herein may provide for an altitude controlsystem that utilizes an air compressor assembly with dynamic axialpreloading for use with an unmanned aerial aircraft, Such features mayaddress the shortcomings associated with failure of the rotating shaftassembly of a motor within the unmanned aerial vehicle due to externalforces to the bearing assembly caused by, for example, backpressure fromwithin an envelope of the balloon, mismatched coefficient of thermalexpansion between the material comprising the driveshaft (for examplesteel) and the material comprising the housing (for example formed ofaluminum), and large temperature changes caused by the environmentsurrounding a device within the unmanned aerial vehicle. In this regard,the features disclosed even eliminate the need to manufacture individualcomponents that separately address these shortcomings.

Example System

FIG. 1 depicts an example system 100 in which an aircraft as describedabove may be used. This example should not be considered as limiting thescope of the disclosure or usefulness of the features of the presentdisclosure. For example, the techniques described herein can be employedon various types of aircraft and systems. In this example, system 100may be considered a “balloon network” though in addition to balloons thenetwork may include other types of aircraft including other airships,etc. As such, the system 100 includes a plurality of devices, such asballoons 102A-F, ground base stations 106 and 112 and links 104, 108,110 and 114 that are used to facilitate intra-balloon communications aswell as communications between the base stations and the balloons. Oneexample of a balloon is discussed in greater detail below with referenceto FIG. 2 .

Example Balloon

FIG. 2 is an example balloon 200, which may represent any of theballoons of the system 100. As shown, the balloon 200 includes an outerenvelope 210, a payload 220 and a plurality of tendons 230, 240 and 250attached to the outer envelope 210. The balloon outer envelope 210 maytake various forms, In one instance, the balloon outer envelope 210 maybe constructed from materials such as polyethylene that do not hold muchload while the balloon 200 is floating in the air during flight.Additionally, or alternatively, some or all of outer envelope 210 may beconstructed from a highly flexible latex material or rubber materialsuch as chloroprene. Other materials or combinations thereof may also beemployed. Further, the shape and size of the outer envelope 210 may varydepending upon the particular implementation. Additionally, the outerenvelope 210 may be filled with various gases or mixtures thereof, suchas helium, hydrogen or any other lighter-than-air gas. The outerenvelope 210 is thus arranged to have an associated upward buoyancyforce during deployment of the payload 220.

The payload 220 of balloon 200 may be affixed to the envelope by aconnection 260 such as a cable or other rigid structure. The payload 220may include a computer system (not shown), having one or more processorsand on-board data storage. The payload 220 may also include variousother types of equipment and systems (not shown) to provide a number ofdifferent functions. For example, the payload 220 may include variouscommunication systems such as optical and/or RF, a navigation system, apositioning system, a lighting system,) a plurality of solar panels 270for generating power, a power supply (such as one or more batteries) tostore and supply power to various components of balloon 200.

In view of the goal of making the balloon outer envelope 210 aslightweight as possible, the balloon envelope may be comprised of aplurality of envelope lobes or gores that have a thin film, such aspolyethylene or polyethylene terephthalate, which is lightweight, yethas suitable strength properties for use as a balloon envelope. In thisexample, balloon outer envelope 210 is comprised of envelope gores210A-210D.

Pressurized lift gas within the balloon outer envelope 210 may cause aforce or load to be applied to the balloon 200. In that regard, thetendons 230, 240, 250 provide strength to the balloon 200 to carry theload created by the pressurized gas within the balloon outer envelope210. In some examples, a cage of tendons (not shown) may be createdusing multiple tendons that are attached vertically and horizontally.Each tendon may be formed as a fiber load tape that is adhered to arespective envelope gore. Alternately, a tubular sleeve may be adheredto the respective envelopes with the tendon positioned within thetubular sleeve.

Top ends of the tendons 230, 240 and 250 may be coupled together usingan apparatus, such as top cap 201 positioned at the apex of balloonouter envelope 210. A corresponding apparatus, e.g., bottom cap 214, maybe disposed at a base or bottom of the balloon outer envelope 210. Thetop cap 201 at the apex may be the same size and shape as and bottom cap214 at the bottom. Both caps include corresponding components forattaching the tendons 230, 240 and 250 to the balloon outer envelope210.

FIG. 3 is an example of balloon 200 in flight. In this example, theshapes and sizes of the outer envelope 210, connection 260, innerenvelope 310, and payload 220 are exaggerated for clarity and ease ofunderstanding. During flight, these balloons may use changes in altitudeto achieve navigational direction changes, in this regard, the innerenvelope 310 may be a ballonet that holds ballast gas (e.g., air)therein, and the outer envelope 210 may hold lift gas around theballonet. Alternatively, in a reverse ballonet configuration, the innerenvelope 310 may hold lift gas therein and the outer envelope 210 mayhold ballast gas (e.g., air) around the inner envelope 310, and theinner envelope 310 may hold the lift gas therein.

An altitude control system 320 may be positioned at the bottom cap 214of the balloon to effect changes in altitude. FIG. 4 is an examplealtitude control system that includes a (1) air compressor assembly 400;(2) valve assembly 500; and (3) electrical control assembly 600. The aircompressor assembly 400 can include a ballonet shroud 401 that can bedirectly joined to and positioned within an opening in the bottom cap214. The valve assembly 500 can be directly connected to an opening inthe air compressor to regulate the amount of air into and the contentsout of the compressor. The electrical control assembly 600 can bepositioned within an opening to the ballonet shroud 401.

The air compressor assembly 400 of the altitude control system can causeballast gas (e.g. air) to be pumped into the inner envelope 310 withinthe balloon outer envelope 210, which increases the density of theballoon and causes the balloon to descend. Similarly, a valve head 502(see FIG. 4 ) of the valve assembly 500 may retract from the inlet ofthe air compressor and may cause air to be released from the innerenvelope 310 (and expelled from the balloon) in order to reduce the massof the balloon and cause the balloon to ascend. The electrical controlassembly 600 may be mounted at the top of the air compressor assembly400.

Example Air Compressor Assembly

FIG. 5 is an example of air compressor assembly 400, which may be used,as noted above, with the altitude control system 320 of an unmannedaerial vehicle, such as a stratospheric balloon. The air compressorassembly 400 can be used to change the amount of air within an envelope(outer envelope 210 or inner envelope 310) by allowing for an increaseor decrease in the amount of air provided to the envelope. For instance,a compressor assembly can be configured to provide air to thestratospheric balloon at a rate and volume of air that will allow forflight at particular high altitudes. This change of air within theballoon envelope, as well as a change in air pressure caused by thecompressor assembly, can allow for a change in altitude and/ordirection.

As shown in the cross-sectional view of FIG. 6 , the air compressorassembly 400 can include many structural features. For example, the aircompressor assembly can include an inlet 402, an outlet 404, a motor406, and a motor housing 407. The motor 406 and motor housing 407 can bepositioned at the outlet. A diffuser 408 can overlie the motor 406,motor housing 407, a compressor housing 410, and an impeller 412. Acavity 414 or plenum of the air compressor assembly 400 can extendthrough a central portion of the air compressor assembly 400 and thecompressor housing 410. In use, the motor 406 can cause rotation of adriveshaft 418, which is coupled to and causes rotation of the impeller412, to accelerate and compress captured air, thereby causing the air tobecome pressurized.

The compressor housing 410 may be generally cylindrical with a circularcross-section. An entrance or opening 416 at the entrance to the inlet402 of the air compressor assembly 400 can form an intake. Thecompressor housing 410 can define a cavity 414 therethrough to enableair or other fluid to flow into and out of the compressor housing 410and the overall air compressor assembly 400. In one example, the cavity414 extends entirely through the compressor housing 410, with theinterior surface 409 of the compressor housing 410 forming a perimeterof the cavity 414. The opening 416 to the compressor housing 410 canhave an inlet opening diameter D1 that is greater than the diameter ofthe compressor housing 410 at any point along the remainder of thecavity 414. This can allow for greater intake of air at the opening 416to the inlet 402. Although generally illustrated as having a circularconfiguration, the compressor housing 410 may alternatively include anysuitable configuration and need not include a circular cross-section.The compressor housing 410 may be formed of at least one of aluminum,brass, or stainless steel, although other types of material may becontemplated.

The overall shape of the compressor housing 410 can define a generallyhour-glass shaped profile having a circular configuration (e.g., theouter dimension of the compressor housing 410 increases and decreasesalong a longitudinal axis X-X defined through a center portion of thecompressor housing 410.) For example, the compressor housing 410 canextend between a first end 422 at an outermost end of the compressorhousing 410, and an opposing second end 424 at the entrance 416 to thecompressor housing. An intermediate point 423 along the compressorhousing 410 may be positioned between the first and second ends 422,424. The diameter of the compressor housing 410 can therefore vary alongthe longitudinal axis X-X, such that the diameter D1 at the second end424 and entrance to the compressor housing 410 and the diameter D2 atthe first end 422 are both greater than the diameter D3 at theintermediate point 423. This change in diameter may allow for thecompressor housing 410 to transition from a wider area or end near thefirst end 422, to a narrower area at the intermediate point 423, andback to a wider end adjacent the second end 424 along the longitudinalaxis X-X. Although generally illustrated as having a circularconfiguration that corresponds to the circular configuration of adiffuser 408 discussed further below, the compressor housing 410 mayalternatively include any suitable configuration and need not include acircular cross-section.

An impeller may be positioned within and occupy at least a portion ofthe inlet 402 of the compressor housing 410. For example, the impeller412 may be positioned adjacent the intermediate point 423 of thecompressor housing 410 and closer to the first end 422 of the compressorhousing 410. The impeller 412, along with the impeller blades 413, canhelp to draw air into and compress air entering into the compressorhousing 410.

The impeller 412 may be coupled to a motor and driveshaft, which cancause rotation of the impeller 412. The driveshaft 418 may be comprisedof a stiff rigid and strong material to ensure that the driveshaft 418can operate throughout the duration of the vehicle flight, as well aswithstand external forces caused by, for example, extreme changes intemperature, backpressure from the envelope, etc. For example, thedriveshaft may be a stainless-steel driveshaft, but other metals orcombinations of metals may also be utilized. The motor 406 can also beany variety of motor with sufficient torque and speed to drive thesystem. An example torque may be 5 NM, but numerous factors can be takeninto consideration which can change the necessary torque and speed. Insome examples, the motor 406 can be a brushless DC, brushed DC, or anysuitable motor so long as it is paired with a suitable controller tooperate it.

In one example, the motor 406 and motor housing 407 can be positionedwithin the outlet 404 of the air compressor assembly and overlie theimpeller 412. For example, as shown in FIG. 6 , the impeller 412 may bepositioned within the inlet 402 of the air compressor assembly 400, suchthat the impeller 412 is positioned between the motor housing 407 andthe opening 416 of the inlet 402.

The diffuser 408 may have a generally planar configuration with acircular profile, although it is contemplated that the diffuser mayinclude any suitable profile, such as square, rectangular, and oval,amongst others. The diffuser 408 may include a first curved portion 408a that can be attached to the first end 422 of the compressor housing410 and a second curved portion 408 b spaced apart from the first curvedportion 408 a so as to define a passageway 437 therebetween throughwhich air moving through the cavity 414 may freely flow out of thecompressor housing 410 and the overall air compressor assembly 400. Thediffuser 408 can convert the mechanical work done by the motor 406 andimpeller 412 of the air compressor assembly 400 back into potentialenergy in the form of air pressure. For example, the diffuser 408 canefficiently convert the kinetic energy of the compressed, flowing airinto higher pressure, static air in the envelope of the balloon.

In use, the motor will rotate the impeller 412 so that the impeller maydraw air into the inlet 402 of the air compressor assembly from thesurrounding environment, for instance the external environment of theballoon. Air entering the impeller 412 will be accelerated through theimpeller 412 and compressed and flow through the passageway 437 of thediffuser 408 and exit the air compressor assembly.

Example Dynamic Axial Preloading Mechanism for an Air Compressor BearingAssembly

As noted above, when the unmanned aerial vehicle is in flight, thevehicle will be subject to extreme environmental changes. The bearingsof the compressor assembly can fail due to unloading caused, forexample, by backpressure from the envelope and/or the forces on thedriveshaft of the compressor assembly of the altitude control assemblycaused by differing rates of thermal expansion. To address this problem,the compressor assembly can be provided with a preloading mechanism tocompensate for changing loads on the driveshaft and bearings. Accordingto aspects of the disclosure, an example altitude control system mayinclude a dynamic axial preloading mechanism for the rotating shaftassembly of a compressor of an unmanned aerial vehicle. The preloadingmechanism can include a flexible backplate which is configured to exerta preloading force onto the bearing assembly of a compressor assembly.Additionally, the motor housing can be designed to minimize rotordynamicstiffness.

A compressor assembly which includes the axial preloading mechanismdisclosed herein may be the air compressor assembly 400 configurationshown in FIGS. 5-6 , but alternative compressor assemblies utilizing apreloading mechanism are contemplated within the scope of thedisclosure. For ease of discussion, the preloading mechanism and motorhousing 407 will be discussed in the context of the air compressorassembly 400, but other types of compressor assemblies can also beutilized in connection with the preloading mechanism and motor housing407 disclosed herein.

With reference to FIG. 7 , an enlarged view of a portion of FIG. 6 ,some of the structural features of the air compressor assembly 400 andparticularly the motor housing 407 and the components housed within themotor housing 407 are first discussed in further detail. In thisexample, the motor housing 407 can overlie the impeller 412 at theoutlet 404 of the air compressor assembly 400. As shown, the motorhousing 407 can include an exterior wall 428 and an interior wall 430that extends upwardly from an interior surface of the exterior wall 428,The interior wall 430 of the motor housing 407 can be positioned betweenthe motor 406 and the exterior wall 428 of the motor housing 407 so asto create an interior space 431 in the area between the exterior wall428 and the interior wall 430.

The motor housing 407 may be comprised of a stiff rigid material, In oneembodiment, a stiff rigid material may be comprised of aluminum that hasa modulus of elasticity of at least 68 GPa. In other examples, themodulus of elasticity may range from 68 to 72 GPa. In still otherexamples, the aluminum may fall outside of this range. Additionally,numerous other types of materials may be used in place of aluminum.

The interior wall 430 and all components of the motor housing 407 may beintegrally formed with the exterior wall 428, such that the motorhousing 407 is monolithic. In other examples, the motor housing 407 maybe formed from one or more individual components that together form themotor housing. Forming the motor housing 407 as a monolithic housinglimits movement between separate and individual pieces that can togetherform the housing. This monolithic structure further increases overallrigidity/stiffness of the motor housing 40.

The driveshaft 418 can extend through a central portion of the motorhousing 407 and the overall air compressor assembly 400. A first end 417of the driveshaft 418 can be coupled to a backplate 442. A second end419 of the driveshaft 418 can extend beyond an exterior edge 429 of themotor housing 407. A portion of the second end 419 may extend beyond theexterior wall 428 of the motor housing and may be coupled to theimpeller 412.

At least one bearing assembly may be used to provide rotation of thedriveshaft 418. In one example, two bearing assemblies can be coupled tothe driveshaft 418 and positioned within the interior wall 430 of themotor housing 407. A first distal bearing assembly 434 and a secondproximal bearing assembly 432 may help to provide rotation of thedriveshaft 418. The first distal and second proximal bearing assemblies434, 432 may be ball bearing assemblies, but other types of bearingassemblies can also be utilized with the driveshaft 418.

The first distal bearing assembly 434 may be positioned at a first end417 of the driveshaft 418 and seated within the backplate 426. The firstdistal bearing assembly 434 can include a first inner race 450 thatextends around the driveshaft 418 and is positioned directly adjacentthe driveshaft 418. A second outer race 452 can extend around both thefirst inner race 450 and driveshaft 418. A plurality of balls 455 may bepositioned between the first inner race 450 and the second outer race452, so that the first and second inner races 450,452 are spaced apartfrom one another. The first inner race 450 may be attached to thedriveshaft 418, so that the second outer race 452 can freely rotateabout the first inner race 450.

A second proximal bearing assembly 432 can be positioned between thefirst end 417 and second end 419 of the driveshaft 418. The secondproximal bearing assembly 432 can be seated within an outermost end ofthe motor housing 407 and is adjacent the second spacer 438. Like thefirst distal bearing assembly, include a first inner race 458 thatextends around the driveshaft 418 and is positioned directly adjacentthe driveshaft 418. A second outer race 460 can extend around both thefirst inner race 458 and driveshaft 418. A plurality of balls 465 may bepositioned between the first inner race 458 and the second outer race460, so that the first and second inner races 458, 460 are spaced apartfrom one another. The first inner race 458 may be attached to thedriveshaft 418, so that the second outer race 452 can freely rotateabout the first inner race 450.

Additional components may be coupled to the driveshaft, including afirst spacer 436 and a second spacer 438. The first and second spacermay be are respectively positioned adjacent the first distal bearingassembly 434 and the second proximal bearing assembly 432. One or moremagnets 440 can be positioned between the first and second spacers436,438. The first spacer 436 may be directly adjacent and abut thefirst distal bearing assembly 434 and the second spacer 438 may bedirectly adjacent and abut the second proximal bearing assembly 432. Theinterior space 431 can be filled with an epoxy or other insulant to helpminimize the heat generated by the motor.

The first curved portion 408 a of the diffuser 408 may be joined to atop edge 427 of the motor housing 407, and a backplate 424 may overliethe top edge 427 of the motor housing 407. Attaching the backplate 442to the motor housing 407 encloses the interior space 431 within themotor housing 407.

The air compressor assembly 400 may include a dynamic axial preloadingmechanism. In one example, the dynamic preloading mechanism includes thebackplate 442. The backplate 442 may be circular and extend around thecircular base circumference of the motor housing 407 so as to close offan outer end of the motor housing 407. The backplate 442 may include anexterior surface 444, an interior surface 446 that faces toward theinterior space 431 of the motor housing. In one example, the bearingseat 470 may be integrally formed with the backplate 442.

The backplate 442 may be a flexible backplate designed to achieve radialstiffness. For example, this can be accomplished by designing thebackplate 442 to have a high aspect ratio, where a width W of thebackplate 442 is substantially greater than its thickness T. Forexample, the back plate may be have a width W that is at least 50 timesgreater than the thickness T. An example width W may be and an examplethickness may be 77 mm wide and 1 mmm thick. In other examples, thewidth may range from 35 to 350 mm and the thickness range from 0.35 mmto 3.5 mm In still other examples the width W may be less than 50 timesgreater than the thickness T provided the backplate is configured toflex. Similarly, the width W may be more than 50 times greater than thethickness T.

The backplate 442 can be formed from a material that is capable offlexing at extreme temperatures without the material failing. Forexample, the backplate 442 may be formed from spring steel, aluminum, orother materials with suitable material properties including tensilestrength and elongation at yield. The backplate 442 may be formed fromany suitable manufacturing process which yields the desired materialproperties, including conventional methods, such as milling, extrusion,molding, casting, etc.

A seat that overlies the backplate can be used to seat the first distalbearing assembly 434. In one example, bearing seat 470 can be integrallyformed at a central portion C of the backplate 442. The bearing seat 470can alternatively be separately formed and coupled or attached to thebackplate 442. As shown in FIG. 8 , an enlarged view of a portion ofFIG. 7 , a circumferential wall 472 of the bearing seat 470 extendsupwardly from the interior surface 446 of the backplate 442. The bearingseat 470 is sized to receive and seat the first distal bearing assembly434. An interior surface 474 of the bearing seat 470 can be generallyu-shaped to complement the shape of the first distal bearing assembly434. An interior edge or interior ridge 476 can divide the interiorsurface 474 into a lower interior edge surface 474 a and an upperinterior edge surface 474 b. The upper interior edge surface 474 bextends in a direction above the interior ridge 476 and away from thedriveshaft 418, whereas the lower interior edge surface 474 a extends ina direction below the interior ridge 476 and closer to the driveshaft418. A corner or shoulder 482 is formed where the interior ridge 476extends laterally away from the lower interior edge surface 474 a andwhere the lower interior edge surface 474 a extends vertically away fromthe interior ridge 476.

When the first distal bearing assembly 434 is seated within the bearingseat 470, the shoulder 482 of the bearing seat 470 may contact thesecond outer race 452. For example, the top surface 454 of the secondouter race 452 can be in contact with the interior ridge 476 of thebearing seat 470. The lower interior edge surface 474 a of the bearingseat 470 can contact the edge surface of the second outer race.

Referring back to FIG. 6 , screws 488 may extend around thecircumferential edge to secure the backplate 426 to the motor housing.But, in other examples, different or additional forms of attachment mayalso be used, As shown in FIG. 9 , an enlarged view of a portion of FIG.6 , when the backplate 426 is secured to the motor housing, the interiorsurface 446 of the backplate 442 can contact the circumferential topedge surface 486 of the exterior wall 428 of the motor housing 407.Additionally, an interior edge surface 448 of the backplate 442 candirectly abut the circumferential top edge surface 486 of the exteriorwall 428 of the motor housing 407. When the backplate 442 flexes, theinterior edge surface 448 of the backplate 442 will be caused to moveeither downward in a direction D or upward in a direction U relative tothe circumferential top edge surface 486 of the motor housing 428,depending on whether the backplate 442 is expanding or contracting.

During flight, the air compressor assembly may be used to change thealtitude and direction of the unmanned vehicle. The motor 406 may causerotation of the driveshaft 418 and the impeller 412. The impeller 412may draw air from the environment surrounding the altitude controlsystem into the inlet 402 of the air compressor assembly 400 and throughthe central cavity and into an envelope, such as outer envelope 210and/or inner envelope 310. When the unmanned vehicle is at highaltitudes, such as in the stratosphere, the temperature of the airsurrounding the unmanned vehicle, as well as the air drawn into thecompressor, and into the envelope, may be extremely cold.

To ensure that the bearing assembly remains engaged throughout theflight, a preloading force can be applied to the distal bearing of themotor to keep the desired preloading force consistent despite changes inthe mechanical stack-up of the assembly. For example, the backplate 442,including bearing seat 470 (which may be integrally formed with thebackplate 442), can apply the necessary preloading force to the firstdistal bearing assembly 434. Due to changes in temperature, for instancebetween different altitudes, as well as other external forces, thebackplate 442 will be caused to flex, thereby applying an axialpreloading force on the top and radial surface of the distal bearingsalong a top surface of the distal bearing. Additionally, the flexure canbring the interior surface of the seat, closer together with the motorhousing 407.

For example, the backplate 442 may apply both an axial and radial forceonto the first distal bearing assembly 434, As shown in FIG. 8 , theinterior bottom surface 478 of the backplate 442 can apply an axialforce F onto the top surface 454 of the second outer race 452 of thefirst distal bearing assembly 434. In particular, the surface 480 of theinterior ridge 476 faces toward the second outer race 452 and can exerta force F onto the second outer race 452. The lower interior edgesurface 474 a of the backplate 442 can also apply a lateral or radialforce R onto the edges surface 453 of the second outer race 452. Theaxial force F, and radial force R help to ensure that the first innerand second outer races 450,452 of the first distal bearing assembly 434remain engaged.

The axial force F exerted onto the first distal bearing assembly 434 mayalso cause a force to be exerted onto the second proximal bearingassembly 432. Referring back to FIG. 6 and the enlarged view in FIG. 10, the axial force F can cause an axial force to be applied by the motorhousing 407 onto the second proximal bearing assembly 432. For example,a force “Fproximal” can be applied to the bottom surface 456 of thesecond outer race 460 of the second proximal bearing assembly 432. Thiswill cause the first inner race 458 and second outer race 460 of thesecond proximal bearing assembly 432 to remain engaged.

When flexed, the backplate 442 may further slightly bow in the middle atthe bearing seat 470 due to the fact that the circumferential perimeterof the backplate 442 is fixed to the motor housing 407. This can causethe outer circumferential edge 484 of the backplate 442 to move in adirection D (FIG. 9 ) so that the interior surface 446 of the backplate442 adjacent the circumferential top edge surface 486 of the motorhousing 407 is moved closer to the motor housing 407, and the interioredge surface 448 of the backplate 442 moves closer to edge 490 of themotor housing 407. Such movement may be a distance that is in micronsand not visible to the eye. In one example, the movement may be adistance of 500 microns, but in other examples, it can be more or less.At differing temperatures, the flexible plate will continue to flexcloser to, as well as away from the motor housing 407. This in turn,allows for an increase or decrease in any space between the backplate442 and the motor housing, as well. as an increase or decrease in thepreloading force applied to the distal bearing.

The attachment of the backplate 442 to the motor housing 407 may alsoprovide support to the motor housing 407, so that a motor housing 407can be used to house the motor 406 and withstand the high velocities ofthe rotating driveshaft 418. The motor housing 407 may be a rigid motorhousing.

Thus, use of the features of the dynamic axial preloading mechanism of acompressor assembly of an altitude control system can provide rigidsupport for the rotating assembly, while applying preload across a verywide temperature range. Such features address the shortcomingsassociated with failure of the rotating shaft assembly of a motor withinthe unmanned aerial vehicle due to external forces to the bearingassembly caused by, for example, backpressure from within the envelope(including outer envelope and inner envelope), mismatched coefficient ofthermal expansion between the driveshaft (for example formed of steel)and compressor housing (for example formed of aluminum), and largetemperature changes caused by the environment surrounding a devicewithin the unmanned aerial vehicle. This can help to prevent thecatastrophic failure that would result from unloading the bearing athigh speed. The features therefore compensate for changes in atmosphere,backpressure, temperature, etc. that would otherwise cause bearingassembly failure. By keeping the bearings preloaded, the life of thealtitude control device can be extended. Moreover, the backplate 442provides rigid radial support for the rotating assembly to ameliorateany undesirable rotordynamic effects, Use of a preloading mechanism toaddress these issues results in a mechanism that has no moving parts andcan serve as the distal bearing support without needing clocking oranti-rotation mechanisms. Furthermore, the features disclosed eliminatethe need to manufacture individual components that separately addressthese shortcomings.

Most of the foregoing alternative examples are not mutually exclusive,but may be implemented in various combinations to achieve uniqueadvantages. As these and other variations and combinations of thefeatures discussed above can be utilized without departing from thesubject matter defined by the claims, the foregoing description of theembodiments should be taken by way of illustration rather than by way oflimitation of the subject matter defined by the claims. As an example,the preceding operations do not have to be performed in the preciseorder described above. Rather, various steps can be handled in adifferent order or simultaneously. Steps can also be omitted unlessotherwise stated. In addition, the provision of the examples describedherein, as well as clauses phrased as “such as,” “including” and thelike, should not be interpreted as limiting the subject matter of theclaims to the specific examples; rather, the examples are intended toillustrate only one of many possible embodiments. Further, the samereference numbers in different drawings can identify the same or similarelements.

What is claimed is:
 1. An altitude control system for an aerial vehicle,the altitude control system comprising: a motor coupled to a driveshaft;a bearing seat; a bearing assembly positioned in the bearing seatconfigured to facilitate axial rotation of the driveshaft; a flexibleplate coupled to the bearing seat; wherein the flexible plate isconstructed to flex in response to changes in temperature and apply aforce to the bearing seat and a preloading force to the bearing assemblythat changes in response to changes in temperature, and wherein theflexible plate is constructed to compensate for differences in rates ofthermal expansion experienced at altitudes of 18 to 25 kilometers abovesea level.
 2. The system according to claim 1, wherein the bearingassembly comprises a ball bearing assembly that includes a first innerrace directly adjacent the driveshaft and a second outer race spacedaway from the first inner race, wherein the flexible plate is directlyadjacent the second outer race and the bearing seat applies thepreloading force to the second outer race when the flexible platecompensates for differences in thermal expansion.
 3. The system of claim1, wherein the bearing seat includes a circumferential wall extendingupwardly from a surface of the flexible plate and forming acircumferential perimeter around a portion of the surface of theflexible plate; the bearing seat sized to secure the bearing assemblywithin the circumferential wall.
 4. The system of claim 1, wherein thebearing seat transitions from a first diameter adjacent a surface of theflexible plate to a second diameter that is greater than the firstdiameter, wherein an interior ridge is formed at the transition betweenthe first and second diameters, and wherein the bearing assemblycontacts the interior ridge.
 5. The system of claim 1, wherein theflexible plate is attached to a motor housing.
 6. The system of claim 1,wherein the flexible plate is attached to a motor housing along aperimeter of the flexible plate.
 7. The system of claim 1, furthercomprising an impeller coupled to an end of the driveshaft, the impellerconfigured to draw air into a compressor housing.
 8. The system of claim7, wherein the compressor housing further comprises an inlet and anoutlet, wherein the impeller is positioned at the outlet, and whereinthe motor housing overlies the impeller.
 9. The system according toclaim 1, further comprising an outer envelope configured to retain liftgas therein and an inner envelope disposed within the outer envelope,the inner envelope being configured to retain a ballast gas therein,wherein a compressor assembly regulates an amount of air within theinner envelope.
 10. The system according to claim 1, further comprisingan outer envelope and an inner envelope disposed within the outerenvelope, the outer envelope configured to retain a ballast gas therein,wherein the compressor assembly regulates an amount of air within theouter envelope.
 11. The system according to claim 6, wherein the motorhousing is open at one end and includes an opening, and wherein theflexible plate extends across the opening, so as to enclose an interiorspace of the motor housing.
 12. The system according to claim 1 whereinthe flexible plate is constructed to compensate for differences in ratesof thermal expansion experienced at high altitudes at or above 18kilometers
 13. An altitude control system for an aerial vehicle, thealtitude control system comprising: a motor coupled to a driveshaft; abearing seat; a bearing assembly positioned in the bearing seatconfigured to facilitate axial rotation of the driveshaft; a flexibleplate coupled to the bearing seat, wherein when the flexible plate is ina first position, the flexible plate applies a first preloading force tothe bearing seat and the bearing assembly, wherein in response to achange in temperature, the flexible plate is constructed to move into asecond position, the flexible plate applying a second preloading forceto the bearing assembly in the second position that is different thanthe first preloading force, wherein the flexible plate is constructed tomove and change bearing preload in response to change in temperatureexperienced due to altitude change to compensate for differences inrates of thermal expansion experienced at altitudes.
 14. The systemaccording to claim 13, wherein the bearing assembly is a ball bearingassembly that includes a first inner race directly adjacent thedriveshaft and a second outer race spaced away from the inner race,wherein the flexible plate is directly adjacent to the bearing seat andapplies the first and second preloading force to the second outer racewhen the flexible plate compensates for differences in thermalexpansion.
 15. The system according to claim 13, wherein the bearingseat includes a circumferential wall extending upwardly from a surfaceof the flexible plate and forming a circumferential perimeter around aportion of the surface of the flexible plate; the bearing seat sized tosecure the bearing assembly within the circumferential wall.
 16. Thesystem according to claim 13, wherein the bearing seat transitions froma first diameter closer to the surface of the flexible plate to a seconddiameter that is greater than the first diameter, wherein an interiorridge is formed at the transition between the first and seconddiameters, and wherein the bearing assembly contacts the interior ridge.17. The system according to claim 13, further comprising an outerenvelope and an inner envelope disposed within the outer envelope, theouter envelope configured to retain a ballast gas therein, wherein acompressor assembly regulates an amount of air within the outerenvelope.
 18. The system according to claim 13, further comprising anouter envelope configured to retain a lift gas therein and an innerenvelope disposed within the outer envelope, the inner envelope beingconfigured to retain a ballast gas therein, wherein a compressorassembly regulates an amount of air within the inner envelope.
 19. Thesystem according to claim 13, wherein the compressor assembly furthercomprises an impeller coupled to the driveshaft, and a motor housingoverlies the impeller.
 20. The system according to claim 13 wherein theflexible plate is constructed to move and change bearing preload inresponse to change in temperature due to an altitude change at highaltitudes.